How much iodine do pregnant and breastfeeding women need?

Iodine is an essential nutrient that humans need in very small quantities. A small gland in the neck, known as the thyroid, uses iodine to produce thyroid hormones.¹ These hormones are vital to ensure normal development of the brain and nervous system before birth, in babies and young children.^2,3 For this reason, it is very important that pregnant and breastfeeding women get enough iodine. Humans store iodine in the thyroid.¹ As only small amounts can be stored, any excess is excreted.⁴

The National Health and Medical Research Council (NHMRC) and the New Zealand Ministry of Health recommend that women who are pregnant have 220µg of iodine per day. Women who are breastfeeding should have 270µg per day.¹ The World Health Organization (WHO) recommends women who are pregnant or breastfeeding take a daily oral iodine supplement so that the total daily intake is 250µg.⁵ Pregnant and breastfeeding women need to top up their dietary iodine intake because of the increased requirements during pregnancy and breastfeeding and the likelihood that they won’t get enough from their diet and mandatory fortification.

What foods contain iodine?

Most foods in Australia contain only small amounts of iodine, making it difficult for pregnant and breastfeeding women to get enough iodine through food alone. The amount of iodine varies greatly based on factors such as changes in season and processing practices. Fortified bread, dairy and seafood are the main dietary sources of iodine in Australia.

Why do pregnant and breastfeeding women need more iodine than other population groups?

Humans store iodine in the thyroid. In pregnancy, the thyroid is particularly active, producing about 50 per cent more thyroid hormones than usual.³ To produce enough thyroid hormones to support the mother and fetus, the mother needs to increase her iodine intake.

If iodine intake is inadequate before pregnancy, the mother’s stores may run low and be inadequate to support the unborn baby in later stages of pregnancy.⁶ The production rate of thyroid hormone returns to normal when breastfeeding. However, NHMRC recommends that breastfeeding women also take an iodine supplement because breast fed infants are completely dependent on milk as a source of iodine and need around 90 to 100µg of iodine per day.¹ Infants use this iodine to build their own reserves of thyroid hormones.^7,8

Are pregnant and breastfeeding women getting enough iodine?

No. The weighted results from the National Iodine Nutrition Survey suggest the median urinary iodine concentration in Australia is 96µg/l which, according to WHO, suggests that the Australian population is mildly deficient.⁹ There are limited studies specific to the iodine status of pregnant women in Australia, but those available prior to fortification suggest it was inadequate.⁹

Why has this occurred?

Reasons suggested for the recurrence of iodine deficiency in Australia include reduced use of iodine-based cleaning products by the dairy industry and reduced household use of iodised salt (caused by a gradual increase in consumption of commercially processed foods containing non-iodised salt).¹⁰

What happens if pregnant and breastfeeding women do not get enough iodine?

The main health concern of mild iodine deficiency during pregnancy anad breastfeeding is its negative effect on the brain and nervous system of unborn children and infants, in particular reduced intelligent quotient (IQ).^11,12,13,14

When iodine intake falls below recommended levels the thyroid cannot produce enough thyroid hormones and a range of iodine deficiency disorders can occur.^1,15 Iodine deficiency is of particular concern during pregnancy because abnormal function of the mother’s thyroid has a negative impact on the nervous system of the unborn baby, and increases the risk of infant mortality.3 Adverse effects on early brain and nervous system development are generally irreversible and can have serious implications for mental capacity in later life.¹⁶

I know bread has recently been fortified with iodine. Do pregnant and breastfeeding women need a supplement as well?

Yes. Mandatory fortification is where food manufacturers are required to add a vitamin or mineral to a food. Mandatory iodine fortification has been introduced in Australia and New Zealand as an initiative to improve public health. Bread made in Australia, where salt is used, except bread represented as organic, is now required to contain iodised salt, instead of non-iodised salt. ‘Bread’ includes not only bread but also rolls and hamburger buns and other bread products.

Through mandatory fortification, most of the Australian population will get enough iodine¹⁷, meaning women of child-bearing age should enter pregnancy with adequate iodine intake. However, the extra iodine available through bread is not enough to meet the additional needs of pregnancy and during breastfeeding.¹⁸ Therefore, NHMRC recommends that women who are pregnant, breastfeeding or considering pregnancy take an iodine supplement of 150µg each day. Supplements of 150µg/d of iodine are safe and effective for pregnant and breastfeeding women.

Are iodine supplements safe for all women?

Women with pre-existing thyroid conditions should seek advice from their medical practitioner prior to taking a supplement.

Is it possible that by taking an iodine supplement pregnant and breastfeeding women will have too much iodine?

No. In Australia, where the population is only mildly iodine deficient, taking an iodine supplement at the recommended dose of 150µg/day will not lead to an excessive iodine intake. However, monitoring of intake to ensure levels don’t exceed the recommendation is included in the mandatory iodine fortification monitoring framework and will be conducted by the Australian Institute of Health and Welfare.

Are there any benefits of taking supplements with more than 150µg iodine?

No. NHMRC recommends supplementation of 150µg/day to ensure that all women who are pregnant, breastfeeding or considering pregnancy have adequate iodine status. As only small amounts of iodine can be stored, any excess is excreted.

How was the level of supplementation determined?

The level of supplementation was determined using data on average iodine intakes post mandatory bread fortification, based on knowledge that the Australian population is now classified by WHO as mildly iodine deficient.^19,20

Are there some iodine supplements that women who are pregnant, breastfeeding or planning pregnancy should not take?

Yes. Women should not take kelp (seaweed) supplements or kelp based products because they contain varying levels of iodine²¹ and may be contaminated with heavy metals such as mercury. In addition, a survey of 15 prenatal supplements available in Australia found iodine contents of between 150 and 270µg, with one leading brand containing no iodine.²² Pregnant and breastfeeding women are advised to check that their vitamin and mineral supplements include the recommended amount of iodine and should consider taking supplements designed specifically for pregnancy and breastfeeding.

When should women start and finish taking iodine supplements?

Women should take iodine supplements from the point of planning pregnancy through the full duration of pregnancy and breastfeeding. If pregnancy is not planned, women should start taking an iodine supplement as soon as possible after finding out that they are pregnant.

How was this statement developed?

NHMRC developed this Statement via a review of the literature and consultation with an expert group. The review, Iodine supplementation during pregnancy and lactation, is available at www.nhmrc.gov.au . The evidence supporting this Statement will be reviewed in time and the Statement revised as necessary. Members of the expert group were Professor Katrine Baghurst, Professor Colin Binns, Professor Peter Davies, Professor Creswell Eastman and Dr Dorothy Mackerras.

Reprinted with permission. Original available online.